• Every major animal phylum that exists on Earth today, as well as a few more that have since become ex:nct, appeared within less than 10 million years during the early Cambrian evolu:onary radiaon, also called the Cambrian explosion. • Phylum Brachiopoda is represented by the brachiopods, marine animals that have calcareous or chi:no- phosphac shells, or valves, that surround a variety of internal organs and muscles. Brachiopod valves are hinged at the rear, while the front can be opened for feeding or closed for protec:on. In a typical brachiopod a stalk-like pedicle projects from an opening called a foramen in the larger ventral valve, aaching the animal to the seabed but clear of silt that would obstruct the opening. • Brachiopods have an epithelial mantle that secretes and lines the shell, and encloses the internal organs. The brachiopod body occupies only about one-third of the internal space inside the shell, nearest the hinge. Like bryozoans, brachiopods have a lophophore, a coil of tentacles whose cilia create currents that enables them to filter food par:cles out of the water. Unlike bryozoans, brachiopod lophophores are non-retractable and occupy up to two-thirds of the internal space, near the front where the valves gape when opened. • Some brachiopods have a calcareous brachidium that supports the lophophore. Terebratula Spiriferina Zeilleria • Two major groups of brachiopods are recognized, ar:culate and inar:culate. Arculate brachiopods have toothed hinges and simple muscles for opening and closing the two valves, while inar:culate brachiopods have untoothed hinges and a more complex system of muscles used to keep the valves aligned. • Brachiopods possess a bilateral symmetry across their dorsal and ventral valves, unlike the pelecypods which have bilateral symmetry between their two valves. • Brachiopods are arguably the most important group of fossil animals. They arose in the Early Cambrian and flourished during the Paleozoic Era. Their diversity was remarkable — over 12,000 fossil species are known — yet there are only about 350 species alive today. • Class Inar:culata • Class Ar:culata • Order Lingulida • Order Orthida • Order Acrotre:da • Order Strphomenida • Order Pentamerida • Order Rhynchonellida • Order Spiriferida • Order Terebratulida • Order Lingulida (E. Cam.-Rec.): The • Order Acrotre:da (E. Cam-Rec.): The lingulids have biconvex shells that acrotre:ds have mostly circular are nearly all chi:no-phosphac. shells that are chi:no-phosphac or The pedicle emerges posteriorly calcareous. The pedicle emerges between the valves without a through a foramen in the ventral special foramen. Example is Lingula. valve. Example is Orbiculoidea. Lingula Orbiculoidea • Class Inar:culata • Class Ar:culata • Order Lingulida • Order Orthida • Order Acrotre:da • Order Strphomenida • Order Pentamerida • Order Rhynchonellida • Order Spiriferida • Order Terebratulida • Order Orthida (E. Cam.-L. Perm.): The orthids have subcircular to semiellip:cal, generally biconvex shells with straight hinge lines and radial ribs. The foramen notches the edge of both valves. Examples include Dinorthis (Ord.), Rhapidomella (Dev.), and Tropidoleptus (Dev.). Dinorthis Rhapidomella Tropidoleptus • Order Strophomenida (E. Ord.-E. Jur.): The strophomenids have shells with one valve convex and the other flat or concave. The hinge lines are straight. Foramen are very minute or lacking. Examples include Rafinesquina (Ord.), Leptaena (Sil.), and Chonetes (Dev.). Rafinesquina Leptaena Chonetes • Order Pentamerida (M. Cam.-L. Dev.): The pentamerids have heavy, generally smooth, strongly biconvex shells with short hinge lines. An internal spondylium, a spoon-shaped calcareous muscle support, is variably developed. Examples include Kirkidium (Sil.), Pentamerus (Sil.), and Stringocephalus (Dev.). Kirkidium Pentamerus Stringocephalus • Order Rhynchonellida (M. Ord.-Rec.): The rhynchonellids have biconvex shells that usually have strong radial ribs and very short hinge lines. They have well- developed foramen. Examples include Rhynchotrema (Ord.), Rhynchotreta (Sil.), and Camarotoechia (Miss.). Rhynchotreta Rhynchotrema Camarotoechia • Order Spiriferida (M. Ord.-L. Jur.): The spiriferids have shells that have either rounded, very short hinge lines or extended hinge lines. Foramen are always present and a spiral brachidium is usually well-developed. Examples include Atrypa (Dev.), Athyris (Dev.), and Mucrospirifer (Dev.). Atrypa Athyris Mucrospirifer • Order Terebratulida (E. Dev.-Rec.): The terebratulids have shells with very short, rounded hinge lines. Foramen are present as are looped brachidia. Examples include Terebratula (Jur.), Oleneothyris (Pal.), and Calloria (Rec.). Terebratula Oleneothyris Calloria • Phylum Mollusca includes seven classes of animals: • Amphineura • Pelecypoda • Gastropoda • Conularida • Pteropoda • Scaphopoda • Cephalopoda • Mollusca include marine, freshwater, and terrestrial animals. Most of them have an exoskeleton or a shell of some kind secreted by the mantle. They are all free-moving and swim, crawl, or burrow. The body consists of a head (except in the pelecypods), a foot, and a dorsal por:on which includes the internal organs and is covered by the mantle. They have well- developed circulatory, diges:ve, excretory, and nervous systems. Respiraon is carried out by gills. • The phylum is pelecypod represented by over 60,000 living species and many thousands of fossil gastropod ones, but only the pelecypods (bivalves), gastropods (snails), and the cephalopods (squids, nau:loids, and ammonoids) have an abundant fossil record. cephalopod • The pelecypods, also known as bivalves, are represented by clams, muscles, and oysters, among others. They are nearly all marine. They have a calcareous shell of two valves with bilateral symmetry between the valves. Valve growth begins at an ini:al point, a beak or umbo, and proceeds outward concentrically. • Pelecypod valves are lateral, or le_ and right. They are mirror images of each other, with the plane of symmetry between the valves. • Pelecypod valves are closed by muscles and opened by hinge ligaments when the muscles relax. Teeth along the hinge aid in ar:culaon. The shell is made up of several layers. The external layer is the periostracum, a thin, flexible, dark-colored layer composed of a protein called concholin. The periostracum protects an underlying calcareous layer which is composed of an outer prismac calci:c layer and an inner porcellaneous or pearly aragoni:c layer made up of thin subparallel lamellae. Jacobs et al. (2008) • Locomoon in pelecypods is accomplished by a hatchet- shaped foot capable of burrowing. An incurrent or branchial siphon draws in water bringing food to the mouth and oxygen to the gills; an excurrent or anal siphon carries off the waste products and water that has passed over the gills. Eyes are present in some pelecypods such as the scallop Pecten. • Pelecypods occupy a wide range of habitats and are found in :dal zones to water as deep as 17,000 feet. Some are free-swimming, like the scallop Pecten. Grill and Zuschin (2001) • Pelecypods are found in the fossil record in the Cambrian, but they are quite rare un:l the Late Cambrian. They rapidly diversified during the Ordovician and Silurian. Examples include Orthonota (Dev.), Pecten (Carb.), Ostrea (Tri.), and Mercenaria (Jur.), among many others. Representaves of many of these genera are alive today. Orthonota Pecten Ostrea Mercenaria • The rudists were among many bizarre pelecypods that evolved during the Mesozoic Era. They arose during the Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms. The rudists went ex:nct at the end of the Cretaceous. • The gastropods are represented by the snails, single-valved mollusks, and include marine, freshwater, and terrestrial forms. • The general anatomy of gastropods is similar to that of pelecypods, but they differ from pelecypods in having a more or less dis:nctly marked head which usually bears tentacles, eyes, and ears and usually contains a large Terrestrial gastropod cerebral ganglion. Marine gastropods would have a gill in place of a lung. • Gastropods are both herbivorous and carnivorous. Their mouth contains a radula, a minutely toothed, filelike, chi:nous ribbon, which is typically used for scraping or cung food before the food enters the esophagus. Some gastropods use their radula to bore into other shelled animals, while others, such as cone snails, secrete toxins and use them as poisoned harpoons. • Many marine gastropods are burrowers and have a siphon that extends out from the mantle edge through a Siphon siphonal canal. A siphon enables the animal to draw water into their mantle cavity and over the gill. They use the siphon primarily to “taste” the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers. • The embryonic shell is called the protoconch. The shell grows as a gradually widening cone which is Posterior wound around an axial pillar, the columella, or around a central tubular cavity. Each coil is known as a whorl. The last whorl, in which the animal lives, is known as the body whorl; all of the other whorls together form the spire. The aperture varies in form and it may be closed by a calcareous or chi:nous plate, the operculum, aached to the posterior part of Anterior the foot. • Whether conical or saucer- shaped, gastropod shells are Sinistral Dextral usually coiled into a spiral which is either right-handed (dextral) or le_-handed (sinistral). The coiling is the result of the more rapid growth of one side of the gastropod’s body, and as it is usually the le_ side which grows more rapidly than the right, the dextral coil is the more common type. • The shell is oriented by Sinistral Dextral holding it so that the apex (posterior end) is above and the aperture (anterior end) is below facing the observer. • In a dextral shell, the aperture is on the right side; in a sinistral shell, the aperture is on the le_ side. These are two species in the genus Neptunea. • Gastropods exceed all classes of mollusks in variety and importance. There are more than 30,000 known species, of which more than 20,000 are recent.